Question 1

How do I set up PTF to test a P4 switch with veth interfaces?

Accepted Answer

Follow the README example: use veth_setup.sh to create interfaces, compile the switch, and run PTF with --interface options mapping ports to veths (e.g., --interface 0@veth1). Ensure Python bindings are included via --pypath for control-plane integration.

Question 2

PTF or OFTest: which is better for my project?

Accepted Answer

PTF is dataplane-agnostic and ideal for testing forwarding behavior independent of control protocols, while OFTest is specialized for OpenFlow. Choose PTF if you need protocol flexibility or are not using OpenFlow, as PTF evolved from OFTest with added features.

Question 3

How can I run PTF tests in parallel?

Accepted Answer

Use the sharding feature: run multiple PTF instances with --num-shards and --shard-id to split tests. For example, with three shards, run separate processes with shard-id 0,1,2 to distribute the test load across hosts or cores.

Question 4

What licensing issues should I consider with PTF's packet modules?

Accepted Answer

Scapy uses GPL v2.0, which may require your test code to be GPL-compatible, while bf_pktpy is Apache 2.0 for permissive use. Choose bf_pktpy to avoid copyleft, but be aware of its limited packet manipulation capabilities.

Question 5

How to write a custom filter in PTF to ignore specific packets?

Accepted Answer

Define a Python callable that takes a Scapy packet and returns True to keep or False to discard. Add it using testutils.add_filter() in your test setup, as demonstrated in the sai_base_test.py example for filtering IPv6 packets.

Question 6

Can PTF test multiple switches simultaneously?

Accepted Answer

Yes, PTF supports multi-device testing by specifying device numbers in interface mappings (e.g., --device-socket for nn platform) and using device-aware functions like send_packet with (device,port) tuples, enabling validation of networked topologies.

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